Determining or verifying the chemical compositions of various materials and articles, in particular because of the increasing complexity of the materials that are used in industry and because of a desire to be environmentally friendly (recycling, health inspections, . . . ), has led to inspection and measurement techniques being developed that are usable on site and in real time and that avoid taking away samples and sending the samples to analysis laboratories.
The techniques that are presently available comprise spark spectroscopy, X-ray fluorescence spectroscopy, and laser-induced plasma spectroscopy.
In summary, spark spectroscopy devices, which generate a plasma by means of an electric arc between the material to be analyzed and an anode through which an electric pulse is caused to pass, suffer from the essential drawbacks of not being portable, of requiring samples of the materials to be prepared, of operating only with materials that conduct electricity, and of requiring contact with the material being analyzed, thus making the use of that technique difficult or even impossible on moving articles, articles at high temperature, or articles located in an environment that is contaminated, difficult, or dangerous.
X-ray fluorescence devices are portable, but they are suitable for measuring only those elements that are lighter than silicon. They need to be put into contact with the materials of the articles to be analyzed and they are the subject of safety constraints and regulations.
In practice, they do not enable measurements to be made on grades of aluminum that differ from one another in terms of silicon or magnesium, or on steels for which it is necessary to measure carbon content, or on organic compounds based on carbon, hydrogen, nitrogen, and oxygen.
Existing laser-induced plasma spectroscopy devices, also known as laser-induced breakdown spectroscopy (LIBS) devices, are essentially laboratory appliances that are perhaps transportable, but that are never portable and self-contained, essentially because they use laboratory laser generators that are large in size and bulky, and because they involve a series of spectrometers for analyzing the spectral components of the plasma in various wavelength ranges. Incorporating a plurality of spectrometers in such appliances increases their cost and their weight. In addition, the useful signal received by each spectrometer is no more than a fraction of the useful signal emitted by the plasma, thereby degrading the photometric balance and harming measurement sensitivity.
Furthermore, in those known plasma spectroscopy devices, the laser generator is often connected to a measurement probe by an optical fiber, which means that it is not possible to convey high levels of laser energy at wavelengths shorter than 532 nanometers (nm) and that it is not possible to take measurements on plastics materials or on organic compounds for which it is preferable to use an ultraviolet laser beam having a wavelength of 266 nm. Furthermore, the optical fiber degrades the radiance of the laser beam (where radiance is its energy divided by the product of the emission area and the emission solid angle), such that it is more difficult to focus the beam on the material or the article to be analyzed and it becomes necessary to take measurements in contact with the article or to increase the size of the optical components used, thereby giving rise to an increase in their bulk and their cost.